1. Field of the Invention
The present invention relates to the production of a liquid crystal display device.
2. Description of the Related Art
A liquid crystal display device comprises a pair of substrates and a liquid crystal inserted between the substrates. One substrate is a TFT substrate forming TFTs, and the other one is a color filter substrate forming color filters. An annular seal comprising a photo-curable sealing agent is formed on one substrate. After the pair of substrates are bonded together, the annular seal is irradiated with ultraviolet rays so as to be cured. The liquid crystal is inserted into a region surrounded by the annular seal.
In a conventional method of producing a liquid crystal display device, an injection hole is formed in the annular seal, the liquid crystal is injected through the injection hole formed in the annular seal in a vacuum chamber after the substrates are bonded together. Thereafter, the injection hole in the annular seal is closed, and a liquid crystal panel comprising the pair of substrates is taken out from the vacuum chamber.
In producing the liquid crystal display device in recent years, there has been proposed a drip injection method (see, for example, Japanese Unexamined Patent Publication (Kokai) No. 2001-133795). In the drip injection method, an annular seal is formed on one substrate, and droplets of liquid crystal is dripped into the annular seal of one substrate. Then, the pair of substrates are bonded together in the vacuum chamber. According to the drip injection method, the injection of liquid crystal is completed at the same time as the substrates are bonded together, reducing the steps of production and lowering the cost of producing the liquid crystal display device.
In Japanese Unexamined Patent Publication (Kokai) No. 2001-133795, a rectangular seal having openings at four corners is provided, instead of a rectangular annular seal, the liquid crystal is dripped onto the area surrounded by the seal, and thereafter, the liquid crystal leaking from the openings are wiped and the openings are then sealed with a sealing member. Further, polar spacers are provided between the pair of substrates.
When the temperature of an environment in which the user is using the liquid crystal display device rises or drops, however, the volume of the liquid crystal filled in the liquid crystal display device expands or contracts, and the cell space of the liquid crystal display device becomes no longer capable of tolerating or absorbing a change in the volume of the liquid crystal. In the liquid crystal display device, for example, vacuum bubbles tend to be contained in the liquid crystal in the frame portion between the pixel display area and the annular seal. In an environment in which the user uses the liquid crystal display device, it is possible that the bubbles flow into the pixel display area from the frame portion due to a drop in the temperature of the environment causing a shading in the display. In producing the liquid crystal display device, therefore, the liquid crystal is used in slightly larger amounts so that the bubbles will not remain in the frame portion. When the temperature of the environment rises, however, expansion of the liquid crystal cell becomes no longer capable of dealing with the amount of expansion of the liquid crystal. When the liquid crystal display device is used in a nearly upright position, therefore, the excess of liquid crystal stays in a lower position of the liquid crystal display device due to the weight, and the thickness of the cell of this portion becomes irregular.